INTRODUCTION Q1 
flagellate type (Fig. 4a), consisting of a head, largely 
made up of chromatin, a middle piece, and a vibratile 
tail. Spermatozoa are comparatively minute, rang- 
ing in size from those of Amphioxus, which are less 
than 0.02 mm. long, to those of 
the amphibian, Dvscoglossus, 
which reach a length of 2.0 mm. 
According to Wilson it would 
take from 400,000 to 500,000 
sea urchin spermatozoa to equal 
in volume the egg of the same 
species. It is not surprising, 
therefore, to find that the num- 
ber of spermatozoa produced by 
a single male may be hundreds 
of thousands times as great as 
the number of eggs developed | 
inafemale. Eggs are, as a rule, 
incapable of locomotion, but 
spermatozoa are active, swim- 
ming about by means of their 
tails until they reach the passive 
eggs which they are to fertilize. : 
; Fic. 4a.— Diagram of a 
Since generally only one sperm- flagellate spermatozodn. 
atozodn fuses with an egg, it is "72" Wuson, 1900.) 
obvious that most of them never perform the function 
for which they are specialized; but apparently an 
enormous number are formed to make the fertiliza- 
tion of the eggs more certain. 
The experiments of Loeb and Bancroft (1912) on 
spermatozoa have shown that when the living 
Apical body or acrosome, 
Nucleus. 
End-knob. 
Middle-piece. 
Envelope of the tail. 
Axial filament, 
End-piece, 
